What were the limitations of Dobereiner's classification?

Limitations of Dobereiner's classification:
$\left(i\right)$ They were not applicable for very low mass or very high mass elements.
$\left(ii\right)$ All the elements couldn't fit into Dobereiner's triads.
$\left(iii\right)$ As the methods to calculate atomic mass improved, Dobereiner's triads validity began to decrease.
For example, in the triad of $F,Cl$ and $Br$, the arithmetic mean of atomic masses of F and Br are not equal to the atomic mass of $Cl$.